Sitecore Commerce installation package comes with Sitecore Business Tools SDK.
If you are planning to custommise Business Tools you might have to setup the development environment for Business Tools. You can find more information on how to setup the development environment here
For each version of Sitecore Commerce you need to install the specific version of Business Tools in you development environment.
See below the compatibility table for Business Tools with Sitecore commerce-
Package for the same can be found here